CHARACTERIZING CRYPTIC FAULTS ACROSS THE NORTHERN WALKER LANE/BASIN AND RANGE TRANSITION ZONE, CALIFORNIA AND NEVADA

Active faults distributed across the northern Walker Lane/Basin and Range transition zone north of Reno, Nevada accommodate approximately 8-14% (~4-7 mm/yr) of the Pacific/North American relative plate boundary shear. The majority of this strain is accommodated across well-defined and well-characterized northwest striking right-lateral strike-slip faults. However, transtensional deformation is also accommodated by relatively shorter left-lateral, normal, and oblique faults and an unknown amount of shear is transferred to the western Basin and Range. Many of these faults are poorly characterized, and some are included in the National Seismic Hazards Map. Several factors that complicate defining fault rupture parameters along these faults include slow slip rates, short paleoseismic records, slip partitioning, and distributed, branching, and/or conjugate rupture patterns. These factors are further complicated by a pervasive geomorphic resetting of the landscape due to climatic fluctuations that has resulted in the burial of many fault traces by Quaternary deposits (pluvial and glacial) that are often younger than fault recurrence intervals. Thus, enigmatic rupture parameters have limited our understanding of recurrence, slip per event, and maximum rupture lengths, important parameters for empirically estimating maximum magnitudes in seismic hazard assessments. Here I summarize recent paleoseismic studies from across the region that highlight these complications. The faults include the Dog Valley, Petersen Mountain, Fred’s Mountain, Spanish Springs Valley, Bonham Ranch, and San Emidio faults. These studies provide incremental details on the regions seismic potential, however much work remains to better define fault rupture parameters to adequately assess the hazard on individual faults in the region.